Method and equipment for growing crystals



Sept. 9, 1958 r 5.1. wElss I 2, 51,341

METHOD AND EQUIPMENT FOR GROWING CRYSTALS Filed July 8, 1953 4 Sheets-Sheet 1 I INYENT'OR ,S'lur'fey [may M21155 .ATI'ORN EYS 7 P 9,1958 Q s. l. WEI-SS 2,851,341

v METHOD AND EQUIPMENT FOR GROWING CRYSTALS Filed July 8; 195's 4 Sheets-Sheet 2 ATTORNEYS Sept. 9, 1958 |.---wE|ss I 1,

METHOD AND EQUIPMENT. FOR GROWING CRYSTALS Filed July 8, 195a 4 Sheets-Sheet s 69 4 4 I 9 6'- 27 a 63 79 v o 26 ATTORNEYS Sept 9, 1958 Filed July. a. 1953 82 I. WEISS METHOD AND EQUIPMENT FOR GROWING CRYSTALS 4 Sheets-Shea. 4

VII/J 'IINVIENTOIR,

United States Patent METHOD AND EQUIPMENT FOR GROWING CRYSTALS Shirley I. Weiss, New York, N. Y. Application July 8, 1953, Serial No. 366,770 11 Claims. (Cl. 23-301) This invention relates to the art of crystal growing, and more particularly to a method and equipment for growing a crystal of semi-conductive material.

In the manufacture of devices containing semi-conductive solid state material designed, for example, to function as rectifiers and amplifiers in the manner of conventional vacuum tubes, it is essential that the electrical characteristics of all the devices manufactured, be predeterminable within given tolerances so they may be used for definite purposes.

According to one method of manufacture of such devices, crystals of say, germanium, are grown by placing the lower end of a seed of such material having the desired molecular arrangement, against the top surface of a melt of the same material. The melt is treated with a material such as arsenic or gallium, hereinafter referred to as doping material, having donor and acceptor characteristics respectively, the quantity of such material which enters the melt determining the resistivity of the latter. The seed is then simultaneously rotated, lifted and vibrated so that a crystal will grow at the lower end thereof having characteristics determined by the type and quantity of the material and the conditions under which it is formed.

Where the seed is lifted as by means of an element such as a cord or tape attached thereto and advanced by a suitable motor, due to expansion and contraction of such element, the rate of growth of the crystal may not be constant with resultant unpredictable variations in its resistivity from one portion to another.

Where the seed is vibrated as by means of a suitable unit reacting against the tape or cord to cause proper growth of the crystal as it is drawn from the melt, as the vibration of the cord or tape may not be constant due to minute irregularities therein, and expansion and contraction thereof, the characteristics of the resultant crystal will also be unpredictable.

Where the doping material which may be in the form of a pellet having the desired donor or acceptor characteristics, is dropped onto the top surface of the melt of semi-conductive material and attached to the growing crystal itself rather than dispersing into the melt to dope the latter, no transformation of the melt will occur, with the result that the crystal will be useless for its intended purpose.

Where the doping pellet to be added to the melt is volatile and is placed on the top surface of the melt, as a portion of such pellet will volatilize and not enter into the melt, the resistivity of the crystal may not be that desired, based upon the quantity of the doping material added.

Where the doping pellet is dropped onto the top sur- In the manufacture of a crystal for junction transistors, illustratively transistors of the N-P-N type, in which the thickness of the P layer determines the electrical characteristics of the device, where a pellet of P type material, such as gallium, for example, is dropped onto the top surface of the melt of germanium which has previously been doped with arsenic, for example, to have donor or N type characteristics, due to the surface tension of such melt, the rate of dissolving of the gallium into the melt is undetenninable with the result that when the melt is subsequently doped to transform it back to have N type characteristics, the P layer may not be of the desired thickness.

Where the doping pellets to transform the melt to P and back to N type characteristics are dropped onto the top surface of the melt, the momentary cooling of the top surface of such melt due to the cool pellet also affects the diffusion rate with consequent effect on the thickness of the P layer.

Where the -doping pellet added to the top surface of the melt is irregular in shape, the rate of melting of such pellet may vary depending upon the particular position in which it falls, which also affects the thickness of the P layer.

In addition, where the pellet is dropped onto the top surface of the melt, the miniscus of such melt will also interfere with immediate diffusion of the pellet which results in the unpredictability of the resistivity of the crystal and the thickness of the P layer.

Where in the manufacture of the crystal, an operator observes an indicator which shows the length of crystal growth and at a predetermined length effects a manual operation which causes a doping pellet to be dropped onto the melt, the possible anticipation or lag caused by such manual operation may result in the pellet being added at not precisely the moment desired, so that the resultant crystal does not have the desired characteristics.

It is accordingly among the objects of the invention to provide a relatively simple method and correspondingly simple equipment for growing crystals of semiconductive material having any desired predetermined characteristics within given tolerances.

Another object is to provide an equipment for growing crystals of the above type which will provide vibration of the crystal at a desired frequency and withdrawal of the crystal from the melt without the need of tapes or cords, and with assurance that the rate of withdrawal of the crystal will be substantially constant, and which enables doping material to be added to the melt in such manner that the doping materialwill rapidly and substantially completely disperse through the entire melt, with assurance that such pellet will be added substantially exactly when desired, based upon the length of the crystal growth so that the crystal will have the predetermined desired characteristics, which equipment is not likely to become deranged even with long use and which requires substantially no supervision other than initial charging with the desired material.

According to the invention from its broadest aspect, a receptacle is provided having a cavity in which a charge of semi-conductive material may be positioned, the cavity adjacent its floor having an inlet connected by a passageway to the top of the receptacle so that a pellet of doping material may be added to the contents of the cavity. The receptacle may be heated to a temperature sufficient to melt the charge of semi-conductive material, preferably by means of a conventional induction heating unit.

Means are preferably provided to rotate a seed of semiconductive material of the same type as that in the cavity, and to vibrate and lift such seed, which is preferably in the form of a bar. To this end a vertical shaft is rotatably mounted on a slidable support, desirably moved by means 3 of amotor driven screw which extends through a correspondingly threaded opening in said support, the rate of vertical movement of said support and the shaft thereon being determined by the speed of the motor and the pitch of the screw. The shaft is desirably rotated at ,a predetermined rate of speed by means of a suitable motor which continuously rotates said shaft even while the support is being raised by its associated motor.

Means are desirably provided at the lower end of the shaft to atfix one end of a crystal seed thereto, the lower end of said seed being normally positioned against the top surface of the melted charge in the cavity. Associated with the shaft and also mounted on the support therefor, is a vibrator mechanism which may comprise a motor rotating an eccentric wheel which oscillates a pivoted arm, the free end of which straddles the shaft and is designed to abut against a collar affixed thereon so that the shaft will vibrate at the frequency of the vibrating arm.

The shaft desirably extends through a plate having at least one opening therethrough connected by a suitable conduit to the passageway in the receptacle. Rotatably mounted on the shaft adjacent the top surface of the plate is a feed wheel, which has at least one opening normally out of register with the opening in plate and designed to receive a doping pellet. The feed wheel desirably'has a gear fixed thereto normally meshing with a pinion driven by a suitable feed motor.

A counting mechanism is associated with the equipment which indicates the distance of travel of the support and hence of the shaft so that the length of the grown crystal may readily be ascertained by inspection of the counting mechanism. Through a suitable electric switch controlled by the counting mechanism, the feed motor may be turned on and off, the counting mechanism being settable to actuate such switch at any desired length of crystal growth. Thus, based on the setting of the counting mechanism, when the crystal has grown a predetermined amount, the feed motor will be actuated to rotate the feed wheel to bring the opening therein into registry with the opening in the plate so that a doping pellet of desired characteristics will thereupon be discharged through the conduit into the passageway leading into the inlet of the cavity and by reason of the rotation of the melted contents of such cavity, the pellet will immediately be drawn into such contents and melted substantially instantly to diffuse therethrough.

In the accompanying drawings in which are shown one or more of various possible embodiments of the several features of the invention,

Fig. 1 is a perspective view of the equipment,

Fig. 2 is a longitudinal sectional view taken along line 22 of Fig. 1,

Fig. 3 is a plan view taken along line 3-3 of Fig. 2,

Fig. 4 is a fragmentary detail view similar to Fig. 2 on a greatly enlarged scale,

Fig. 5 is a view taken along line 55 of Fig. 4, and

Fig. 6 is a view taken along line 6-6 of Fig. 4.

Referring now to the drawings, the equipment desirably comprises a base (not shown) from which rises a vertical post 11 having a horizontal plate 12 affixed to its upper end. A conventional reduction gear unit 13, mounted on the undersurface of plate 12, carries a drive motor 15, the shaft 16 of which extends into unit 13. The output of the reduction gear unit rotates a pinion 17 which, through idler gear 18, rotates main gear 19.

Means are desirably provided to facilitate adjustment of the speed of rotation of main gear 19. To this end, as shown in Fig. 3, a rigid strip 21, having an elongated slot 22 therethrough, is pivotally mounted on plate 12 by means of a screw 23 extending through the slot 22. The strip 21 desirably has an upstanding stud 24 near one end on which the idler gear 18 may be rotatably mounted.

Thus the speed of main gear 19 may be determined by the size of the idler gear 18 and the position of strip 21 may be adjusted by loosening screw 23 so that when the selected idler gear 18 is mounted on stud 24, it will engage both pinion 17 and main gear 19.

The main gear 19 also desirably engages a pinion 26 which, through bevel gears 27, .28 drives a conventional counter 29 to indicate the length of crystal growth, said counter controlling a switch (not shown) for the purposes hereinafter to be described.

Affixed to post 11 beneath plate 12, is a pair of spaced horizontal supporting plates 31 and 32, each having an opening '33 through which the post 11 extends. Vertically mounted between plates '31 and 32 and rigidly affixed thereto in front of post 11 is a substantially rectangular rigid panel 34 which desirably has an elongated vertical slot 35.

Slidably mounted on panel 34 which defines a track, is a substantially U-shaped support 36, the legs 37 of which straddle panel 34. Extending rearwardly from the cross piece 38 of support .36 is an arm 39 having a threaded opening 40 through which extends a vertical screw 41, the latter being positionedbetween panel 34 and post 11.

The lower end 42 of screw 41 rests on a bearing 43 mounted on plate 32 and the upper end of the screw extends through aligned openings 45 and 46 in plates 31 and 12 and has the gear 19 affixed thereon as well as a hand wheel 47. Thus upon rotation of screw 41, the support 36 will be moved vertically, a micro-switch 44 afiixed to plate 31 in the path of movement of the cross piece 38 of the support being actuated thereby, to cut off motor 15 to limit the upward movement of the support.

Extending laterally outward from the cross piece 38 of support 36 near its lower edge are a pair of spaced studs 49 which extend through associated openings 51 in a horizontal plate 52, a set screw 53 extending through plate 52 and engaging one of the studs 49 affording ready adjustment of the position of plate 52 on said studs.

Aflixed to plate 52 at one edge thereof and rising therefrom is .a mounting block 54 which carries an electric motor 55, the shaft 56 .of which extends through the block 54 and has an eccentric wheel 57 mounted thereon substantially midway between the side edges of the cross piece 38 of-support 36 and spaced therefrom.

The wheel 57 is designed to oscillate or vibrate an .arm 58, the inner end of which is positioned between and pivotally mounted as at 59 to blocks 61 affixed to the cross piece 38 near the upper edge thereof. The outer end of arm 59 is desirably bifurcated to form legs 62 which straddle .a vertical crystal carrying shaft 63.

As is clearly shown in Figs. 1 and 2, the upper end 65 of shaft 63 extends through an opening 66 in plate 12, through a bushing .67; through a worm gear 68 which is splined to shaft 63, and through a supporting strip 69 mounted at its ends on studs 70 affixed to plate 12. Although any suitable means may be provided to rotate shaft 63, as illustratively shown in Fig. 3, a motor 78 is mounted on plate 12 and has a worm 79 which engages worm gear 68.

The lower end 71 of shaft 63 extends through a sleeve 72 affixed at its lower end in an opening 73 in a horizontal plate 74 affixed at one end as by screws 75, to plate 32, and such end 71 of shaft 63 desirably has a suitable chuck 76 thereon which serves to hold one end of a crystal seed 77.

In order that shaft 63 may be vibrated by arm 58, yet rotate freely under the drive imparted thereto by motor 78, a bearing 81 is desirably positioned on shaft 63 between arm 58 and a collar 82 affixed to the shaft by set screw 83. To urge the shaft 63 downwardly, a weight 84 is idly mounted on shaft 63, with a resilient washer 85 intervening between the weight 84 and collar 82.

To form the crystal, the lower end 87 of the crystal seed 77 is positioned in a melt of suitable material in a receptacle 88. As shown in Fig. 4, the receptacle is desirably a block of any suitable material which does not react with the contents of the receptacle, in the illustrative embodiment herein being of compressed graphite or carbon particles, especially suitable for use with a semiconductive metal such as germanium.

Although the receptacle, which is preferably cylindrical, may be mounted in any suitable manner, as illustratively shown in Fig. 2, a horizontal table 91 is provided having a lateral hub92 with a vertical opening through which the post 11 extends. The hub 92 has a laterally projecting boss 93 with a vertical bore through which extends one end of an adjustment screw 94. The other end of the screw extends into a gear box 95 affixed to a second hub 96 positioned above hub 92, and which also has a vertical opening through which. post 11 extends. The screw 94 is rotatable by means of a handle 98 to raise or lower table 91 and the hubs 92 and 96 may be secured at any desired position on post 11 by means of locking handles 97 and 99, respectively.

Mounted on table 91 is an inverted box 101, the top wall 102 of which has an opening 103 therethrough, desirably circular as shown. Positioned in the box 101 and resting on table 91 is a block 104 of heat insulating material such as graphite, which desirably has a central opening 105 therethrough aligned with the opening 103 in box 101 and with an opening 106 in table 91.

The top surface 107 of block 104 desirably has an annular groove 108 therein with a washer 110 on its floor which serves as a seat for the lower end of a transparent sleeve 109, preferably ofquartz glass which rises from said block 104, through the opening 103 in box 101 and through an opening 111 in a horizontal plate 112 affixed at one edge as by screws 113 to a flange 114 rigid with hub 96.

The upper end of sleeve 109 may be positioned against a washer 115 in an annular groove 116 in the undersurface of horizontal plate 74, an annular member 117 afiixed' to the undersurface of plate 74 having a beveled inner periphery 118 to guide the upper end of sleeve 109 into annular groove 116.

To support the receptacle 88 on table 91, the upper ends of a plurality of upstanding rods 121 are positioned in sockets 122 in the bottom of the receptacle and the lower ends of said rods are positioned in sockets in said block 104. The receptacle desirably has a substantially cylindrical axial cavity 125 therein,- the floor 126 of which is substantially conical as shown, and a plurality of passageways 127 are provided from the top 128 of the receptacle, said passageways desirably being inclined from the vertical in the direction of rotation of shaft 63 and having their outlets 130 leading into the cavity 125 nearsuchfloor 126.

Although the contents of the cavity 125 maybe heated in any suitablern-anner, in the illustrative embodiment herein shown, an induction heating coil 131 heated by a suitable induction heating unit (not shown) is mounted on the horizontal plate 112 encompassing the sleeve 109 which is free to move through said coil.

Means are desirably provided to regulate the temperature of the contents of the cavity 126. To this end, a thermocouple is provided having a tube 133, the upper end of which extends into a vertical bore 134 in said receptacle 88. The tube 133 desirably extends through and is afiixed in a vertical sleeve 135 clamped in an opening 136 in block 104 and extending through the opening 106 in plate 91. The lower end of the tube 133 which protrudes beyond sleeve 135 extends into a cooling unit 137, desirably a thermos bottle, suspended in any suitable manner beneath plate 91. The terminals of the thermocouple are suitably connected to a temperature control unit (not shown) which in conventional manner controls the application of power to the induction heating coil 131.

Means are desirably provided automatically to add doping material to the contents of the cavity at predetermined intervals.

To this end as shown in Figs. 2, 4 and 5, a plate 141 is mounted on plate 74 and spaced therefrom. The sleeve72 extends through aligned openings in plate 141, a feed wheel 142 and a gear 143, the latter being afiixed on the wheel 142 as by screws 144, so that said wheel and gear rotate in unison. Pivotally mounted on plate 141 as at 145 is a motor 146 connected to a source of current through the switch (not shown) controlled by counter 29, the end of the shaft 147 of said motor carrying a pinion 148 that may engage gear 143 when the motor is pivoted to the position shown.

The wheel 142 adjacent its periphery desirably has a plurality of openings 149 therethrough arranged in a ring, which, when the wheel is turned, may be successively moved into alignment with a plurality of openings 151, illustratively three in number, in plate 141. Thus when pellets of suitable doping material are positioned in one or more of the openings 149 in feed Wheel 142, when such opening is moved into alignment with an opening 151, the pellet will drop therethrough.

Means are provided to guide such pellets into the passageways 127 in receptacle 88. To this end, a plurality of openings 153 are provided in plate 74 substantially aligned with the openings 151 in plate 142. Each of the openings 153 defines a socket in which a ball 154 is positioned, each having a bore through which extends a tube 155 desirably of stainless steel. The balls 154 are desirably retained in any desired position in the associated socket, as by means of a leaf spring 156 afiixed at one end to plate 74 and having its free end pressed against the associated ball, said free end having an opening through which the tube 155 extends.

The protruding upper end of each tube desirably has a funnel 157 affixed therein to guide the pellet which drops through opening 151, into such tube. The lower end 158 of each metal tube 155 desirably fits snugly into the end-of a tube 159 desirably of quartz glass, the other end of which is normally positioned into the enlarged end 161 of an associated passageway 127. To prevent oxidation of the semi-conductive metal in the cavity 127, a suitable inert gas, such as nitrogen for example, may be forced into sleeve 109 throughthe aligned openings 106, 105, the plate 74 desirably having a vent 162 for such gas.

7 In order that the crystal may be cooled rapidly after it is formed, a blower 163 may be mounted on the box 101 to force cool air therein against the lower end of sleeve 109 and through opening 103 against the outer wall of said sleeve to cool the latter.

Operation With the table 91 positioned sutficiently below plate 112 so that the sleeve 109 may be removed from box 101 and the receptacle made readily accessible, the cavity 125 in such receptacle is charged with a predetermined quantity of material, illustratively a semi-conductive metal such as germanium and a crystal seed 77 of the same material is aflixed at one end in chuck 76.

The sleeve 109 is then placed over receptacle 88 so that its lower rim seats against the washer 10 in annular groove 108 in block 104. The table 91 is thereupon raised by rotating handle 98 until the lower ends of tubes 159 seat in the openings 161 in the receptacle, at which time the upper rim of the sleeve 109 will be positioned against the washer 115 in annular groove 116 in plate 74.

The valve controlling the source of inert gas is opened so that such gas will flow through openings 106 and 105 into sleeve 109 and discharge through vent 162. The

heating coil 131 is then energized to melt the contents of p 125, the temperature controlunit (not shown) controlled by thermocouple 133' retainingsuch' temperature within predeterminedlimitst After the eontentsof cavity 125 have become molten; motor "78 is energized to drive worm 79 and gear 68 to rotate shaft 63 and-the crystal seed FF-thereon. The motor 55' is also energized to rotate eccentric wheel 57, thereby vibrating arm 58 and shaft 63, the weight 84-limiting the movement of shaft 63 due to the oscillation of arm 58;

With gear 18 out of engagement with' gear 19- and pinion 17, the hand wheel 47 is rotated in direction to turn screw 41 to effect downward movement of support 36 and the arm 58thereon. Consequently the-shaft 63 will also be lowered, the spliningofsaid shaft to gear 68' permitting such movement.

cavity Thehand wheel 47 is turned until the-lower end of the rotating, vibrating seed 77 engages the topsurface of the molten charge of material in cavity 125. The gear 18'is then moved into engagement with gear 19 and pinion 17 and the counter 29 is set to zero position. As a result of the rotation of shaft 63, the molten charge in cavity 125 will also rotate to effect stirring thereof and a crystal will start to format the bottom of the seed 77.

When the head of the crystal has attainedthe desired thickness, the motor is energized and through pinion 17 and gear 18, the gear 19 and screw 41 will be rotated at a predetermined speed based upon the gear ratio. The rotation of screw 41 will effect verticalupward movement of the support to raise shaft 63 and the crystal seed thereon 77. As the crystal seed is slowly lifted androtated and vibrated, the crystal at the end of the seed-will grow, the length of such growth being indicated on the counter 29 driven 27 and 28.

As the temperature is maintained within desired limits by the themccouple 133 and associated temperature control mechanism and as the rate of lifting the crystal is constant, due to the positive drive through screw 41 and the threaded opening in arm 39, and as the vibration of shaft 63 is maintained within controlled limits by reason of the controlled speed of motor 55 and the weight 84 on the shaft which is considerably heavier than the crystal, the resistivity of the crystal will be substantially constant from section to section for given parameters, of the material in the cavity 175, the temperature, rate of lifting of the crystal, speed of rotation and vibration.-

If it is desired to change the characteristics of the crystal, as for example to form a junction type transistor, the switch associated with the counter may be set-to operate at a predetermined time based upon :the length of crystal grown to complete a circuit to motor 146. Energization of motor 146 will cause feed wheel 142 to turn through the drive from pinion 148 and gear 143 to move the openings 149 in which pellets of desired characteristics have been previously placed, into alignment with the openings 151 in plate 141 so that such pellets will drop into the associated funnels 157, down tubes 155 and 159, into the passageways 127 in receptacle 88.

As the length of time that it takes for a pellet to drop from plate 141 into passageway 127 may-readily by determined, the switch associated with counter 29 may be set so that the motor 146 will be energized sufliciently before the crystal has attained the desired length so that during the time it takes the pellet to fall through tubes 155 and 159 and passageway 127 to the outlet 130 of the latter, the crystal will have attained its desired length.

When the pellet, which for example may be of gallium to. convert the N type charge of germanium to P type, reaches the end of the passageways which are preferably inclined in the direction of rotation of the melt by the shaft 63, they will substantially immediately be drawn into the molten germanium and in turn be melted. Due to the rotation of such melt, the pellet will be also instantly diffused therethrough to convert the melt of the P from gear 19 through gears Asthe feed wheel 143'is being rotated at a predetermined speed by motor 146, based upon'the thickness of the P" layer desired, doping pellets of'the N type may be positioned in openings 149 spaced the desired distance from the openings 149 in which the P, type pellets were placed.

Thus when such second openings are moved into alignment with openings 151, the N type pellets will be discharged into the melt as previously described to convert the latter substantially instantly back to N type.

As the crystal grows and the material in the cavity is drawn therefrom, by reason of the substantially conical floor 126 of cavity, substantially all of the material will be utilized and the bottom of the crystal will more or less taper to a point. After the crystal has been completely grown, the power to the various drive motors may be cut off and the blower 163 energized to cool the sleeve 109 and the contents thereof.

When the temperature has fallen sufiiciently to permit handling, as indicated by a thermometer on the temperature control equipment, the table 91 is lowered by turning handle 98 until it has moved sufficiently to permit access to the chuck 76 for removal of the crystal seed and crystal. The crystal may then be cut off the seed and processed in conventional manner to form the completed devices.

With the method herein described in which the dropping pellets are quickly drawn into the body of the melt, they will dispense almost instantly for quick conversion of the melt to the desired characteristic and as the equipment is substantially automatic in operation andas the rate of vibration, rotation and lifting of the crystal is substantially constant, crystals may be produced in quantity with assurance that such crystals will be substantially identical in characteristics.

As many changes could be made in the above method and'equipment, andmany apparently widely difiercnt embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for growing a. crystal of semi-conductive material comprising receptacle means having a cavity to receive a charge of material from which the crystal is to be formed, means 'for heating said charge of material, seed carrier means adapted to carry a seed of crystal growing material, mounting means for rigidly mounting said seed carrier means relative to said receptacle means including variable coupling means to provide. controlled relative movement between said seed carrier means and said receptacle means, and means for operating said variable coupling means;

2. Apparatus as set forth in claim 1, wherein said variable coupling means includes engageable surfaces movable relatively to-one another to provide saidcontrolled relative movement between said seed carrier means and said receptacle means.

3. Apparatus as set forth in claim 1, wherein said receptacle means includes a receptacle having a passageway disposed for subsurface introduction of doping material into said charge of material inthe receptacle and for merging said doping material and said'charge of material in the receptacle only after said charge of material has been heated to a predetermined condition by said heating means.

4. Apparatus as set forth in claim- 1, wherein said receptacle means includes a passageway for introducing doping material into said charge of material, said passageway having one end directed for subsurface introduction ofsaid doping material into said charge of material and theother end thereof terminating above the level of the charge in the crucible.

5. Apparatus for growing a crystal comprising receptacle means having a cavity to receive a charge of material from which the crystal is to be grown, means for heating said charge of material, seed carrier means to carry a seed of crystal growing material, means for rigidly mounting said seed carrier means relative to said receptaclemeans and for providing controlable coupling means for operatively controlling the withdrawal of said seed carrier means from said receptacle including engageable surfaces movable relatively to one another, and means for operating said controllable coupling means.

6. Apparatus for growing a crystal comprising receptacle means having a cavity to receive a charge of material from which the crystal is to be grown, means for heating said charge of material, seed carrier means to carry a seed of crystal growing material, means for mounting said seed carrier means relative to said receptacle means and for providing a variable coupling therebetween including engageable surfaces movable relatively to one another, and means for operating said variable coupling means, said receptacle means including a passageway for introducing doping material into said charge of material, said passageway having one opening directed for subsurface introduction of said doping material into said charge of material and the other end thereof terminating above the level of the charge of material in the crucible.

7. The method of growing a crystal of semiconductive material which comprises charging a cavity in a receptacle with such material, heating the receptacle until the contents of the cavity has attained a predetermined temperature and has melted, placing the end of a crystal seed in such melt so as to engage the top surface thereof, lifting said seed until the crystal has grown a predetermined amount, and merging a quantity of doping material with the melt below its top surface.

8. The method as set forth in claim 7, and wherein said merging of said quantity of doping material with the melt below its top surface is in accordance with a predetermined program of selectviely adding quantities of doping material.

9. Apparatus for growing a crystal of semi-conductive material comprising receptacle means having a cavity to receive a charge of material, means' for heating said charge of material, seed carrier means adapted to carry a seed of crystal growing material, mounting means for rigidly mounting said seed carrier means relative to said receptacle means and adapted to provide relative movement between said seed carrier means and said receptacle It) means, said mounting means including a supporting structure for said receptacle means, variable coupling means carried by said supporting structure and engaged with said seed carrier means, said variable coupling means including track means, means slidable on said track means, feed means coupling said track means and said means slidable on said track means to control said relative movement between said seed carrier means and said receptacle means, and means for operating said feed 0 means.

10. The method of growing a crystal of semi-conductive material which comprises charging a cavity in a receptacle with such material, heating the receptacle until the contents of the cavity has attained a predetermined temperature and has melted, placing the end of a crystal seed in such melt so as to engage the top surface thereof, lifting said seed until the crystal has grown a predetermined amount, merging a quantity of doping material with the melt below its top surface and proceeding with the growing of said crystal.

11. The method of growing a crystal as set forth in claim 10 and wherein after said quantity of doping material has been added and said crystal has grown a further predetermined amount, other doping material is 5 added to merge with the melt.

References Cited in the file of this patent UNITED STATES PATENTS 1,430,900 Haferkamp Oct. 3, 1922 2,447,672 Smith Aug. 24, 1948 2,562,325 Merritt July 31, 1951 2,591,561 Lester et a1. Apr. 1, 1952 2,631,356 Sparks et al. Mar. 17, 1953 2,727,839 Sparks Dec. 20, 1955 2,727,840 Teal Dec. 20, 1955 FOREIGN PATENTS 512,461 Belgium July 15, 1952 OTHER REFERENCES Lehovec et al.: Apparatus for Crystal Pulling in Vacuum Using a Graphite Resistance Furnace in the Review of Scientific Instruments, vol. 24, No. 8, August 1953.

Bell Tel. Lab. Inc. and West. Elect. Co., Inc., Tran- 4 sistor Technology, vol. 1, chapt. 4 and 7, July 1952. 

1. APPRATUS FOR GROWING A CRYSTAL OF SEMI-CONDUCTIVE MATERIAL COMPRISING RECEPTACLE MEANS HAVING A CAVITY TO RECEIVE A CHARGE OF MATERIAL FROM WHICH THE CRYSTAL IS TO BE FORMED, MEANS FOR HEATING SAID CHARGE OF MATERIAL, SEED CARRIER MEANS ADAPTED TO CARRY A SEEL OF CRYSTAL GROWING MATERIAL, MOUNTING MEANS FOR RIGIDLY MOUNTING SAID SEED CARRIER MEANS RELATIVE TO SAID RECEPTACLE MEANS INCLUDING VARIABLE COUPLING MEANS TO PROVIDE CONTROLLED 